I am needing to add RG6 cabling to a bedroom that currently does not have an outlet. I have no problem connecting the RG6 to the splitter outside my home, feeding into my crawlspace and running the length of the home. The question I have is, once I reach the room I need to add the cabling to, how do I knew exactly where in the floor to drill up?

Meaning - I don't want to drill through the floor, I want it to be a wallfish (which I have experience doing but from coming down the wall from say an attic), so how can I locate exactly where to drill up in order to not go through the floor or the baseboard?

I also have an attic and a crawlspace, is there anyway that connects the crawlspace straight up to the attic that I could possibly run a cable up to the attic then wall fish down to a room up there as well? Maybe somehow follow the chimney up, is that possible?

I've done this before - for rooms that have carpeting I use a long, thin nail and simply drive it into the floor. Then go into the crawl space where I can see the nail and thus know where to drill up into the wall space. For rooms that have hardwood or tile I've removed baseboards and drilled (with a thin drill bit) diagonally into the wall space going down. Then poke a wire through so I can see it from the crawl space - then drill a hole up into the wall space for cabling.
– user20618Jan 25 '17 at 14:21

5 Answers
5

Measure carefully. There are usually plenty of reference points... duct vents plumbing, etc.

Once you've done that, either drill a very small hole to feel for the wall's bottom plate, or run a long screw up through. An assistant on the floor above can help determine if you're off target and warn you.

If you have absolutely no reference points, drive a screw down from above in an inconspicuous location. Have an assistant tap it with a hammer to help you find it. Use it as a reference. If screwing through carpet, be very careful to prevent the carpet from grabbing the screw and zipping out a thread. You could remove a piece of base trim to create a hidden hole.

There's unlikely to be a clean passage from your crawl space to your attic through a wall. You'll probably have 3 wall plates in between, and possibly mid-wall blocking. If it was that easy, it wouldn't be called "fishing". :)

I came up w/ a 'cool trick' (I think so, at least). Get some of those strong, rectangular magnets.. Upstairs, on the edge of the wall, where you want the receptacle to be above, put the magnet on the floor and a heavy weight on it, so it won't move. Then, take some measurements to help you figure out where it'll be, when trying to find it from the other side of the wall/floor/whatever. Then, using one of those telescoping magnetic wands (the ones that're designed to help you pick up screws/nails/etc. from behind furniture or whatever) see if you can find where your first magnet is.

Realize: using this method, you have really found the center of the magnet above - meaning you need to account for 1/2 the width of the magnet + the widths of any additional materials (such as baseboards, wallboards, tile, etc..)

Then you can drill a hole (starting small is always sage advice) and if you've done your measurements and locating correctly, the hole will be inside the wall, precisely where you want it to be.

Additional advice: nails/screws/other-metallic-stuff will attract your magnetic wand (false positives). If you think you found where the magnet is, put a dot or an 'X' w/ a sharpie or something and go flip the magnet upside down. Now your magnetic wand should be repelled from the magnet upstairs. If it's being repelled from the dot you made before, then it's a true positive.

Another note: using this method, it's pretty easy to do a couple of sample spots/dots and use those and a straight-edge to make lines showing you where your walls are on the floor above, but letting you have a relatively precise diagram of where they are as you look up from underneath the floor.

That would have to be a seriously strong set of magnets. The floors in my home are about an inch thick. And don't forget, that you could stick the wand near a nail and think it's the magnet.
– MattJan 25 '17 at 18:42

@Matt Well, sorta strong. I've been able to use this w/ some run-o-the-mill magnets from a hobby shop and the magnetic wand through 1.25" thick 'floor' (subfloor + backer board + tile). The trick is to try to 'balance' the magnetic wand between your thumb and index/middle fingers - then move it around the area you think the magnet is located (those rough measurements I mentioned). Since you're talking about 2 magnets trying to attract(or repel - nail scenario) each other, they don't need to be terribly strong. There's a little subtlety to the approach, but it's worked for me. Hope it helps.
– JaimeJan 25 '17 at 20:03

Cool. It makes sense and avoids drilling. It also gives me another idea which is to use a stud finder and a piece of metal.
– MattJan 25 '17 at 20:10

1

I've done more or less this same thing with a few 75lb pull neodymium magnets and the compass in my phone. Works like a charm even on floors that are 2 inches thick.
– Justin OhmsJan 25 '17 at 20:15

1

Interesting idea. Though I thought stud finders were capacitance based - not magnetic.. (I could be wrong though). That does make me think of another bit of advise for everyone. If you're drilling from the underside of a floor, hoping to get your hole inside the wall above, it's possible you'll be so "lucky" as to put your hole into the bottom of a stud - making the hole useless.. (not that I've ever done that.. :-p) when placing your 'upstairs' magnet, use a stud-finder or some other mechanism to avoid that scenario. As always: start small. poke a wire through it, see if its where you want it
– JaimeJan 25 '17 at 20:20

Here are some suggestions. I've used all of these except the last one which I think would work pretty well.

Locate a power socket as my reference point. You'll know it's there because you'll see the wires going up into the inside of the wall.

Position your outlet on the outer wall since the outer wall is always known. Although, that might not be a good position for it in your room.

Drill a tiny hole from the edge of the wall through and poke a wire down through it. Then go below and locate it. The wall is right next to it.

Locate the piles, often piles are below walls. They may give some clues.

Run the wire up through the inside a built in wardrobe to the ceiling space and then along and down through the wall. You can drill these holes next to the wall inside the wardrobe and poke a piece of string or wire down to find it from below.

You can hide/protect the wire in the wardrobe with conduit. Sometimes, this method is just easier, especially when you lack the tools or in my case I had to do this in an old church building and there was were areas I could not crawl to from below so had to transition the wire to above.

Carefully measure. But this is hard to get right because you need to be sure you are measuring from the right position. 10cm out and my may miss the wall completely.

Another idea, put a strip of steel against the baseboard such as a rafter square and use a stud finder to try to locate that. Since most detectors also sense steel it should find it quite easily. Combined with option 6 above you should be able to locate the wall pretty easily.

Ok heres another option. A compass and magnet. See post by Matthias Wandel here

I've only seen this done, so ymmv, but take the long straight part of a coat hanger. Chuck it in the drill. Cut the other end at a slight angle with side cutters. Drill through in a subtle place. (Maybe between the base and the wall.) Once you're through, there should be enough length for you to landmark in the crawl space.